1. Field of the Invention
The present invention relates to transmissions such as an infinitely-variable-ratio transmission of the toroidal race rolling friction type and relates particularly, but not exclusively, to an arrangement for mounting the centre on the shaft in a manner which maintains a desired degree of flexibility between said discs and the shaft.
2. Discussion of Prior Art
In the above apparatus, a main shaft takes drive from, for example, an engine of an automobile and transmits this drive to two outer discs mounted at proximal and distal ends of the shaft. Drive is taken from two inner discs mounted back to back between the outer discs and are supported on a bearing, the inner diameter of which engages with the shaft such that the discs are free to rotate relative to the shaft. Motion is transferred from the outer discs to the inner discs via a plurality of rollers positioned in toroidal cavities formed by contoured surfaces of the inner and outer discs. One or more of the outer discs is subjected to an axial load such that the rollers make contact with the faces of the respective inner and outer discs in order to transmit power therebetween. Typically the inner discs are output discs and power is transferred from the output discs via, for example, a chain drive to a further transmission component such as an epicyclic gearbox. In an alternative arrangement the inner discs are input discs and power is transferred thereto by a chain drive or similar.
Whilst the above arrangement provides a perfectly acceptable transmission the shaft is subjected to a degree of bending as a direct result of power being transmitted to or from the inner discs via the chain drive. Whilst the degree of bending is well within acceptable limits, it must be accommodated if the integrity of the toroidal cavities is to be maintained.
In order to appreciate the problem outlined above we refer to FIG. 1 from which it will be appreciated that if one or other of the outer discs, 14,16 are tilted relative to the normal alignment axis A, the integrity of the toroidal cavity 26,28 will be compromised.
Such tilting might, for example, take place at high torque transmissions when it is possible that shaft 12 might deflect under the strain. This degree of flexing whilst being relatively small must be accommodated without destroying the integrity of the toroidal cavities. A number of proposals exist for compliantly mounting the outer discs 14,16 but no such proposals are known in connection with the inner disc or discs 18,20. Conventionally, the inner disc or discs 18,20 are mounted on the input 12 by means of a bearing 32 which is positioned such that it is in the same axial plane as the neutral plane of the inner disc or discs (as shown in FIG. 1 and FIG. 2). Under normal circumstances, the end load force to which outer disc 16 is subjected is passed trough the variator via the rollers and the inner discs such that said inner discs are effectively squeezed between the outer discs. Any variation in the position of the outer discs is transmitted to the rollers and thence to the inner discs which, as shown in FIG. 1, are often combined as a single unit. In the position of the rollers as shown in FIG. 1, the force is transmitted along lines L1, L2 and cross the centre line CL of the shaft at an angle xcex8. The particular arrangement of the FIG. 1 design means that the load lines L1, L2 cross the centre line CL as point equidistant from the bearing but significantly axially displaced relative thereto. As a consequence of this geometry, a significant force is transmitted through the rollers in the direction of lines L1, L2 and the inner disc or discs 18,20. This force acts to locate the inner discs in the desired manner whilst said discs are still able to rock about the centre line CL of the shaft such that they maintain the integrity of the two toroidal cavities even when one or other or both of the outer discs are tilted out of plane A.
In the alternative arrangement of FIG. 2 the inner discs 18,20 are axially displaced and a chain drive portion is provided therebetween, load lines L1, L2 are coincident at a point O1 which is within the neutral plane of the discs PD. Once again, bearing 32 is still positioned equidistant between the disc surfaces 18, 20 and on the neutral plane of the discs PD. It will be appreciated that, as a result of the specific geometric arrangement of these discs, the force transmitted through these discs will not be able to locate the inner discs in the desired position as the discs will not be free to rock or pivot about point O1, thus compromising the integrity of the toroidal cavity.
U.S. Pat. No. 1,774,175 provides a variator arrangement in which the central discs are mounted on a common bearing which is off-set from the neutral axis or the central discs. This arrangement does not, however, angle the rollers such that their load lines cross the neutral axis of the support shaft at a common point and does not therefore, benefit from the advantages of the present invention.
It is an object of the present invention to provide a transmission apparatus in which the inner discs are mounted on the shaft in a manner which reduces and possibly eliminates the above phenomenon and thereby ensures the integrity of the toroidal cavities is maintained throughout the full operating range of the variator. Additionally, the present invention aims to accommodate a desired degree of movement of the inner discs in order to provide the desired degree of compliance without adversely affecting the above
Accordingly, the present invention provides a variator transmission apparatus comprising:
a shaft having a neutral axis CL;
a pair of outer discs, mounted on the shaft for rotation therewith;
a pair of inner discs, journalled to said shaft by means of a bearing; and
a plurality of rollers having load lines L1, L2 ad being located in said cavities for transmitting torque between the discs and characterised in that in at least one position of said rollers the load lines L1, L2 cross the neutral axis C1 at a common point O1 and in that the inner discs pivot about a point O2 which is axially displaced relative to common point O1.
In one arrangement the outer discs are input discs and the inner discs are output discs.
In an alternative arrangement the outer discs are output discs and the inner discs are input discs.
Advantageously, the bearing comprises an inner and outer race between which a plurality of bearing operate, said outer race having an inner radius of curvature RB having a centre of origin chosen to facilitate rocking of the inner discs relative to said shaft.
Preferably, a variator as claimed in any one of the preceeding claims in which the radius RB is such as to allow free rocking of said inner discs without interference from said bearing.
Alternatively, the radius RB is such as to allow a rocking of said inner discs whilst providing some resistance thereto.
Conveniently, the inner discs comprise axially displaced discs connected to each other and a power drive is connected between said inner discs.
Advantageously, said inner discs in the same plane as the plane PB of the bearing.
Conveniently, a chain or belt drive connects to said inner discs by means of a plurality of teeth provided on or associated with said inner discs.